JOURNAL OF RESEARCH of the National Bureau of Standards - A. Physics and Chemistry Vol. 79A, No. 4. July- August 1975

The Enthalpies of Combustion and Formation of Thianthrene

Walter H. Johnson

Institute for Materials Research, National Bureau of Standards, Washington, D.C. 20234

(May 12, 1975)

The e nthalpy o f combu s lion of thi a nthre ne (diphenylene di sulfid e) has been de te rmin ed in a n oxygen-bo mb ca lorim ete r. The e nth a lp y of form a tion has bee n de rived us ing data from the a vail ab le lit e rature. Th e res ult.s obta ined are as follows:

C" HH5z(c) + 17 0 2(g)+ 228 H 20(liq) = 12 CO 2(g) + 2[1-1 ,50 ., + ll5 H 20] (Iiq)

ilm(25°C)=-7253 .27 ± 1.40 kJ / mol (- 1733 .65 ± 0.33 kcal/ mo l)

ilHj"(25 °C) = 184.23 ± 1.50 kJ / mol (44.03 ± 0. 36 kca l/mol)

A co mpari son is given of th e res ult s of thi s inves ti gation with th ose of pre vious inv es tiga tors.

Key words: Co mbu st ion; entha lpy ; fo rmation ; heat ; seco nda ry s tandard ; s ulfur co mpound ; thi anthrene.

1. Introduction

This inves ti gation is part of a program on th e selec­tion of secondary thermoche mi c<:!l standards. Because the combustion calorimetry of sulfur-containing CO In­

pounds requires ce rtain special techniques in order to obtain acc urate enthalpy values the re is need for a standard refer ence mate rial which co ntains thi s eleme nt.

Thianthre ne (diphenylene di sulfide) has bee n pro­posed as a secondary standard for organic sulfur co mpounds. It is a solid, crystalline material, stable in moist air, has a very low vapor pressure, forms reasonably good pellets, can be ignited and burned co mpletely without the need for an auxiliary sub­stance and is available in high purity. It has been studied ·e xtensively and th e values obtained by in­de pendent investigators are in good agreement.

In order to obtain reliable data for the heat of com­bustion of s ulfur co mpounds , the bomb cavity must be lined with an inert material to prevent reaction with sulfuri c acid, provision must be made for thor­ough mixin g of the bomb solution following combustion of the sample, and the bomb atmosphere must contain so me nitroge n to pre ve nt the formation of sulfur di oxide [1]. '

1 Fi gu,"cs in brac kets indicate the lit e ra ture refe re nces at the e nd of th e l><Ipe r .

2. Materials

Thianthrene 2

The sa mple was obtained from the Aldric h Che mical Company as sample 12,244-0. It was purified by nine passes through a zone-m elting apparatus in an argon atmosphere; the impurities were concentrated in '/3 of the sample whi ch was rejected. The purified sample was a colorless crystalline materi al which was stable in air and was essentially non-hygroscopic.

An elemental analysis of the sa mple yielded the following values in wt percent :

Found Th eo re t ical

C 66.64 ± 0.06 66.63

5 29.41 ± .20 29.64

Benzoic Acid The be nzoic acid used for the calibration experi­

ments was Standard Reference Material (SRM) 39i.

~ The source uf ce rta in mat eri a ls are ide nti fied ill urde r 10 adeq uatel y s pec ify the ex­per im ent a l procedure. In Ill! case does s uc h ident ifi(,a ti o n impl y reco mme ndation or cnd\ll"se­me nt by the Na tional Bureau of S tan dards . nor does it im ply that the mat e ri als ide ntifie d arc the bes t ava ilab le fur the purpose.

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Oxygen The oxygen was obtained from the Matheson

Company as Ultra-Pure Oxygen _ A certificate of analysis furni shed with the cylinder gave the major impurities in ppm as: Kr, 12_0; N 2 , 3_0; Xe, 0.7 ; and N 20, 0.8.

3. Apparatus and Procedure

The adiabatic rotating-bomb calorimeter, the control system and the method of temperature measurement have been described [2].

A sample of approximately 0.24 g was pressed into a pellet, weighed into a platinum crucible and placed in the crucible support of the bomb which contained 3.000 cm:] of water. A 2-c m length of platinum wire , 0.075 mm in diameter, connected between the elec­trodes so that it was in contact with the sa mple, served as a fus e. The bomb was sealed and filled with 31.62 atm of oxygen without flu shing. The te mperature of filling was determined, the calorimeter jacket was evacuated and the bomb was heated electrically to 24.98 0c. The adiabatic tem pe rature controls were put in to operation and the system left overnight. On the following morning te mperatures were observed at intervals of a few minutes during a 30-min initial rating period. The sam ple was ignited by discharging an 18,000 p,F condenser, previoudy charged to 23 V, through the platinum wire fuse. The bomb was then rotated to mix the bomb solution. Thermal equilibrium was obtained after about 20 min and calorimeter temperatures were observed during a 40-min final rating period. Due to the heating effect of the electri c current through the platinum resistance thermometer, a steady increase in te mperature of approximately 0.001 K/h was observed during the rating periods.

The calorimeter was opened and the bomb removed. In three of the experiments the gaseous contents were passed through a weighed CO 2-absorption tube. The bomb was then opened and the liquid contents trans­ferred to a weighed polyethylene bottle. Weighed aliquots were taken for titration with standard alkali

to determine the total acid. The quantity of nitric acid was take n as the difference between the total acid and the theoretical quantity of sulfuric acid calculated from the mass of sample_

4. Results and Calculations

The result s of the benzoic acid calibration experi­ments are given in table 1. The headings, in the order in which they appear in the tables are described as follows: EEE-Std is the e ffective energy equivalent of the standard empty calorimeter including the bomb and all inte rnal platinum parts except the crucible ; Cv-cant(i) is the heat capaci ty of the initial contents of the bomb including the c rucible, sample, bomb solu­tion , and oxygen; Carr ta tm is a correction applied for deviation of the actual mean temperature of the ex­periment from 26.5 °C; Carr-parts is a correction applied for c hanges in the calorimeter sys tem during the series of experiments; EEE-actual is the effective energy equivalent of the actual calorimeter system at the mean temperature of the experiment ; Temp rise is the obse rved increase in te mperature following ignition of th e sample; Q-tatal is the total quantity of energy released, which is obtained as the product of EEE-actual and the Temp rise; q-ign is the electrical energy used to ignite the sample ; q-decamp HN03 is the calculated quantity of e nergy required to de­compose any nitric acid, form ed from traces of nitrogen in the bomb atmosphere, into gaseous nitrogen, oxygen, and liquid water; q-WC is the Washburn Correction [3] used to correct the actual bomb process to the standard process with all reactants and products in their respective thermodynamic standard s tates at the actual final te mperature; q-carr ta 28°C is a cor­rection applied to correct the standard reaction at the actual final temperature to 28 °C, the selected final temperature; Q-std react is the energy evolved by the standard reaction at 28°C, obtained as the sum of Q-tatal and the energy corrections. Division by the mass of sample yields tJ.U ~ (28°C) in J/ g.

. The calibration experiments (table 1) yield EEE-std

TABLE 1. Results of the benzoic acid calibration experiments

Expt. No. 495 524 52.5 .526 527 .529

EEE·Std ...... ..... . .... .... . J/K. 2.5 19.47 2.519.63 2519.47 2.519.70 2.519.68 2.519.46 Ct>cont(i) . .. .. . .. . .. . ....... . J/K .. 4.82 4.81 4.72 4.73 4.70 4.74 Corr to tm ... .... . .......... . J/K .. 0.08 0.11 0.1.5 0.09 0.10 0.14 Corr·parts .. . . .. . .. .. . ....... J/K .. - .16 .00 .00 .00 .00 .00 EEE·actual. ... .. . ....... ... . J/K ... 2.524.20 2.524.5.5 2.524.34 2524.52 2524.48 2.524.34 Temp rise .. . . ... .. .. . . . ........ K .. 3. 133364 3.108335 3.159280 3.089474 3.100061 3.173467 Q· total. .. .. . . . . . . .... . . . ... .. .. . .J ... - 7909 .24 - 7847. 16 -7975.09 - 7799.44 -7826.05 -8010.91 q- ign .. . .... . .. . . .. ... . . .. . . . . ..... J ... 1.22 1.06 Ll8 0.79 1.11 1.16 q-decomp HNO" .... . . ........ J ... 0.70 0.21 0.30 .47 0.17 0.84 q·WC ....... .... . ....... . .. ... .. . J .. . 6.26 6.20 6.29 6.16 6.13 6.36 q- corr to 28 °C. ... . .. . ....... . . J .. . - 0 .04 - 0.04 -0.06 -0.03 - 0.04 -0.06 Q-std react . ... . . .. . .. . . ...... .. J. .. - 790LlO - 7839.73 - 7967.38 - 7792.0.5 - 7818.67 -8002.62 m.~ .. . ........ ... .. . , ...... . ... . .. .. g . .. 0.299167 0.296843 0.301676 0.295038 0.296046 0.303011 W~(28 °C) . . .. ... . . . ..... . . . J/g ... - 26410.36 - 26410.36 -26410 .36 -26410.36 -26410.36 - 26410.36 Mean , EEE-std ..... ... ... .1 1K ... 2.519 .56 sdm .. .. ............ . .... . . ...... . .... . 0.046

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TABLE 2 . Results of the thianthrene combustion experiments

Expl. No. 533 534

EEE-Std .... .. .. . ......... J/K .. . 2519.56 25 19.56 Cv-cont (i) ...... .............. J /K ... 15.89 20.07 Co rr to tm ........ .. ... .. .... J/ K .. . 0.22 0.21 Co n'-pa rt s .... ..... . .. .. ... J /K .. 3.60 .00 EEE-actual ....... . .... . J /K .. 2539.27 2539.84 Temp ri se ...... .. .......... .... K ... 3.230779 3.217870 Q-total. .. .... ...... .. . .. ..... J . - 8203.83 - 8172.87 q-ign .............. ...... . .... ...J ... 0.91 1.29 q-deco mp HNO". ..... . ... .1 .. 9.39 8.l9 q.WC ..... ...... ..... .. .. . ... .1 ... 4.98 7.00 q-corr to 28 °C . . . . . . . . . . . . J. 0.01 0.01 Q-s td react ..... .. . . ... . .. . ... J . -8188.53 -8156.38 In s······· ·· ······ · ....... . .. .. .. g .. 0.244666 0.243654 W~ (28 °C ) ... .... . ..... . .J /g ... -33468.15 -33475.25 Mean, IlU~ (28 °C ) .. .. .... J/g .. . -33475.21 sdm .......... ............ ...... 2.08

from the certifi cate value for be nzoic acid, thi s value is then used in tabl e 2 to determine I1U~ . The precision un certainty is the standard de viation of the mean which is calculated as V'L112 /n(n - 1) where 11 is the deviation of each value from th e average a nd 11, is the number of ex perim e nts pe rformed.

All calculations were perform ed by co mputer 3 and the values in the tables have been take n directl y from the print-out. Du e to rounding of the individual values from the print-o ut , the results obtained from the tabulated values may differ sli ghtly from the more exact results ot tained by the co mpute r. For the be nzoic acid calibration experim e nts th e values of EEE-std were obtained by an ite rative procedure from th e mass of sample. Th e certified value for be nzoic acid, Standard Refe re nce Material (SRM) 39i under certifi­cate conditions was take n as 26434 J/g; thi s reduces to - 26410_36 Jig for I1UC at 28 °C.

The followin g values were used in the co mputation s

Dens it yl Cp/J 'g - IK- I CU) /J . .,. - 1 . atm - I g 'cm - :l aP ( "

Benzoic Acid 1.32 1.21 - 0.0125 Thianthrene 1.44 1.50 - 0.02

The unit of energy is the joule, for conversion from the conventio nal thermoche mical calorie, one calorie is equivalen t to 4.184 joules. The 1971 table of atomic we ights has bee n used throughout thi s paper [4].

The results of the thianthre ne co mbustion experi­me nts are give n in table 2 and correspo nd to the reaction:

C 2H 8S 2(C) + 17 02(g) + 198 H 20 (liq) = 12 CO 2 (g) + 2[H zS04 + 100 H 2 0](liq) (1)

.1 The com put er progra m urigina ll y prepared by Howard Shomal e of the Naval O rdnance T es l Stalion. C hin a Lake . California. and lat e r modified by C . T. Armstrong and E. J. P rosen of Ihi s bureau fullowing the proced ure of W. N. Hubba rd . D. W. Scoll . and C. Wadding lo n lSI.

536 538 539 543 -

2519.56 2519.56 2519.56 25 19.56 20.08 20.07 20.08 19.84 0.24 0.01 0.06 0.07

.00 .00 .00 .00 2539.88 2539.64 2539.70 2539.47

3.258237 2.991124 3.059317 1.095284 - 8275.52 -7596.37 - 7769.75 -2781.44

0.94 1.20 1.31 0.89 6.62 9.99 7.47 3.61 7.06 6.70 6.82 3.78 0.02 0.00 0.00 - 0.05

- 8260.88 - 7578.47 - 7754. 15 -2773.22 0.246746 0.226366 0.231675 0.082832

-33479.23 -33478.85 -33469.91 -33479.89

I1Uc (28 °C ) =-33475.21 ± 6.4lJ/g =- 7241.20 ± 1. 40 kJ/mol

I1Hc (25 °C ) = -7253.27 ± 1.40 kJ/mol (- 1733 .57 ± 0.33 kcal/mol)

I1H] (25 °C ) = 184.23 ± 1.50 kJ I mol (44. 03 ± 0.36 kcal/mol)

Th e uncertainti es assigned to I1U~ have been obtained by co mbination of 2 sdm for th e calibration experime nts with 2 sdm for the co mbu s tion experi­me nts, 0.01 perce nt for the uncertainty in the certifi ed value for be nzoic acid and 0.01 percent for th e effect of possibl e impurities in th e sample.

Th e un certainty assigned to I1H] was obtained by co mbination of the uncertai nty assigned to I1U ~ with 0.01 perce nt in the valu es taken for th e heats of forma­tion of COz(gas), H 20(liq) , and H 2S0 4(aq) [6].

A comparison of the res ults of thi s inves tigation with other re ported values is give n in table 3. For thi s co mpariso n the res ults have been adjusted to corre­spond to reac tion (2) to co nform to th e other re ported values.

C 12HsS2(C) + 17 0 2(g) + 228 H 2 0(liq) = 12 CO 2 (g) + 2[H 2S0 4 + 115 H 2 0](liq) (2)

I1H g(25 °C ) = -7253 _59 ± 1.42 kJ/mol = -1733.65 ± 0.34 kcal/mol

TABLE 3. Comparison with existing data

Inves tigator

Hubbard, Kat z, and Waddingto n ........ Keith and Mac kie .......... .. Sunner and Lundin ........ ................ . Hu , Yen. and Ge ng .... .. .......... ... .. This inves tiga tion .................. .... .

!:J.HC (25 DC), kcal/mo l

- 1733.15 ± 0. 53 - 1732.87 ± .69 - 1733.29 ± .28 - 1733.40 ± .52 - 1733.65 ± .33

[7] [8] [9, 10] [11]

It is interesting to note th at in all cases the results are within the assigned uncertainty intervals. It would appear, therefore, that thianthre ne would be a com-

563

pletely satisfactory substance for use as a secondary standard in the combustion calorimetry of sulfur­containing compounds.

This work was supported by the NBS Office of Standard Reference Materials.

s. References

[1] Sunn er , S. , Sartryck ur Svensk Kemisk Tidskrift 59, 71 (1946).

[2] Prosen, E. J., and Johnson, W. H. , in preparation. For a partial description of the calorimeter, see G. T. Armstrong and W. H. Johnson NBSIR 73-158 (July 1973).

[3] Washburn, E. W., Bur. Standards J. Res. Nat. Bur. Stand. (U.S.) , 10,525-558 (1933) RP546.

[4] Commission on International Atomic Weights, Pure and Applied Chemistry (1971).

[5] Hubbard, W. N., Scott , D. W., and Waddington, G. , J. Phys. Chern. 58, 152 (1954) .

[6] Wagman , D. D. , Evans , W. H., Parker, V. B., Halow, I. , Bailey, S. M., and Schumm, R. H., Selected Values of Chemical Thermodynamic Properties, Nat. Bur. Stand. (U .s.), Tech. Note 270-3, 268 pages (Jan . 1968).

[7] Hubbard , W. N. , Katz , c. , and Waddington , G. , J. Phys. Chern. 58, 142 (1954).

[8] Keith, W. A., and Mackie, H., Trans. Faraday Soc. 54, 353 (1958).

[9] Sunner, S., and Lundin , B., Acta Chern. Scand. 7,1112 (1953). [10] Sunner, S. , Acta Chern. Scand . 17,728 (1963). [11] Hu, J-H. , Yen, H·K. , and Gen g, Y-L. , Acta Chi mica Sinica

32,242 (1966).

(paper 79A4-859)

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